1. Field of the Invention
The present invention relates generally to meter prover apparatus, and more particularly, but not by way of limitation, to an improved uni-directional meter prover apparatus of the type employing a prover barrel through which a piston is propelled by the flow of metered liquid.
2. Description of the Prior Art
Many various types of meter prover apparatus have been developed and used for proving the accuracy of liquid flow meters. Heretofore, prover apparatus have included a prover barrel or loop through which a piston is propelled by the flow of metered liquid. Means for accurately determining the passage of the piston through the loop are provided so that the known quantity of liquid displaced thereby can be compared with the reading of the meter being proved.
In uni-directional types of meter prover apparatus the flow of metered liquid and the piston are directed through the prover barrel in a single direction. An interchange connects the inlet and discharge ends of the prover barrel so that when the piston reaches the discharge end of the prover barrel it is transferred back to the inlet end thereof and the proving cycle is repeated. The transfer of the piston from the discharge to the inlet ends of the prover barrel must be accomplished in a manner such that when the transfer is completed and the piston is launched into the barrel, liquid communication between the ends of the barrel through the transfer system is positively prevented. In addition, means must be provided for retaining the piston between proving runs so that it can be launched into the prover barrel at the discretion of the operator of the apparatus.
While a variety of methods and apparatus for transferring flow propelled pistons from one end of a prover barrel to the other have been developed, such methods and apparatus have generally suffered from the disadvantage that they include complicated and elaborate apparatus, require a number of time consuming manual operations in order to complete the transfer and launching of the piston or are susceptible to leakage and bypassing of the metered liquid through the transfer system whereby inaccurate measurement results. By the present invention, an improved uni-directional meter prover apparatus is provided which is relatively simple, readily lends itself to automatic operation and achieves positive shutoff between the ends of the prover barrel prior to when the flow propelled piston is launched into the barrel.